Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
  • C21D9/525—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length for wire, for rods
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
  • B21B3/02—Rolling special iron alloys, e.g. stainless steel
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES, PROFILES OR LIKE SEMI-MANUFACTURED PRODUCTS OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
  • B21C1/00—Manufacture of metal sheets, wire, rods, tubes or like semi-manufactured products by drawing
  • B21C1/003—Drawing materials of special alloys so far as the composition of the alloy requires or permits special drawing methods or sequences
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21J—FORGING; HAMMERING; PRESSING METAL; RIVETING; FORGE FURNACES
  • B21J1/00—Preparing metal stock or similar ancillary operations prior, during or post forging, e.g. heating or cooling
  • B21J1/02—Preliminary treatment of metal stock without particular shaping, e.g. salvaging segregated zones, forging or pressing in the rough
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/001—Continuous casting of metals, i.e. casting in indefinite lengths of specific alloys
  • B22D11/002—Stainless steels
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
  • C21D1/60—Aqueous agents
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
  • C21D1/613—Gases; Liquefied or solidified normally gaseous material
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
  • C21D8/0226—Hot rolling
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
  • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
  • C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires of ferrous alloys
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/52—Ferrous alloys, e.g. steel alloys containing chromium with nickel with cobalt
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/001—Austenite
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/005—Ferrite

Definitions

• the present invention concerns an austenite-ferrite stainless steel, more particularly one intended for the manufacture of structural elements for materials production (chemistry, petrochemistry, paper, offshore) or energy production facilities, without necessarily being limited to these.
• This steel can more generally be used to replace a stainless steel of type 4301 in many applications, such as in the preceding industries or in the food and agriculture industry, including parts made from shaped wires (welded grids, etc.), profiles (strainers, etc.), axles, etc. One could also make molded parts and forged parts.
• stainless steel grades of type 1.4301 and 1.4307 whose microstructure in the annealed state is essentially austenitic; in the cold-worked state, they can furthermore contain a variable proportion of work-hardened martensite.
• these steels contain large additions of nickel, whose cost is generally prohibitive.
• these grades can present problems from a technical standpoint for certain applications, since they have weak tensile characteristics in the annealed state, especially as regards the yield strength, and a not very high resistance to stress corrosion.
• these austenitic grades have elevated coefficients of thermal conductivity, which means that when they are used as reinforcement for concrete structures they prevent a good thermal insulation.
• low-alloy austenite-ferrite grades have appeared, designated 1.4162, which contain low contents of nickel (less than 3%), no molybdenum, but high contents of nitrogen to make up for the low nickel level of these grades while preserving the desired austenite content.
• nitrogen contents possibly greater than 0.200%, it is then necessary to add high contents of manganese.
• nitrogen levels however, one observes the formation of longitudinal depressions in the continuous casting blooms which, in turn, cause surface defects on the rolled bars, which can be troublesome in certain cases. The manufacture of such grades is thus made particularly tricky due to this poor castability. Moreover, these grades have poor machinability.
• ferritic or ferrite-martensitic are also known whose microstructure is, for a defined range of heat treatments, composed of ferrite and martensite, such as the grade 1.4017 of standard EN10088. These grades, with chromium content generally below 20%, have elevated mechanical tensile characteristics, but do not have a satisfactory corrosion resistance.
• a purpose of the present invention is to remedy the drawbacks of the steels and manufacturing methods of the prior art by making available a stainless steel having, without excessive addition of costly alloy elements such as nickel and molybdenum:
• the present invention provides an austenite-ferrite stainless steel whose composition includes, in % by weight:
• the steel according to the invention has:
• the present invention further provides a method of manufacture of a plate, a band, or a hot-rolled coil of steel according to the invention whereby:
• the method of manufacture of a hot-rolled plate of steel according to the invention involves the steps consisting of:
• the method of manufacture of a hot-rolled bar or wire of steel according to the invention includes the steps consisting of:
• the method according to the invention furthermore includes the following characteristics, taken alone or in combination:
• the duplex stainless steel according to the invention contains the contents defined below.
• the carbon content of the grade is between 0.01% and 0.10%, and preferably below 0.05% by weight. In fact, too high a content of this element reduces the localized corrosion resistance by increasing the risk of precipitation of chromium carbides in the heat-affected zones of welds.
• the chromium content of the grade is between 20.0 and 24.0% by weight, and preferably between 21.5 and 24% by weight, in order to obtain a good corrosion resistance, which is at least equivalent to that obtained with grades of type 304 or 304L.
• the nickel content of the grade is between 1.0 and 3.0% by weight, and is preferably less than or equal to 2.8% by weight.
• This austenite-forming element is added to obtain good properties of resistance to the formation of corrosion cavities. Adding this also helps achieve a good compromise between impact strength and ductility. In fact, it is of interest to shift the impact strength transition curve toward low temperatures, which is particularly advantageous for the manufacture of large bars or thick quarto plates for which the impact strength properties are important. One limits the content to 3.0% because of its elevated price.
• the nickel content is limited in the steel according to the invention, it has been found to be advisable, in order to obtain an appropriate austenite content after heat treatment between 900° C. and 1100° C., to add other austenite-forming elements in unusually elevated quantities and to limit the contents of ferrite-forming elements.
• the nitrogen content of the grade is between 0.12% and 0.20%, and preferably between 0.12% and 0.18%, which generally means that the nitrogen is added in the steel during the production process.
• This austenite-forming element first of all participates in producing a two-phase ferrite/austenite steel containing a proportion of austenite suitable for a good corrosion resistance under stress, but also in obtaining elevated mechanical characteristics. It also makes it possible to limit the formation of ferrite in the heat-affected zone of welded zones, which avoids the risks of embrittlement of these zones.
• One limits its maximum content because, above 0.16% of nitrogen, defects begin to appear in the continuously cast blooms. These defects consist of longitudinal depressions which in turn generate surface defects on the rolled bars, which can be troublesome in certain cases. Beyond 0.18%, the longitudinal depressions are very marked and one further observes blowholes connected with exceeding the maximum quantity of nitrogen which is able to remain in solution in the structure of this grade.
• the manganese content of the grade is between 0.5% and 2.0% by weight, preferably between 0.5 and 1.9% by weight and even more preferred between 0.5 and 1.8% by weight.
• This is an austenite-forming element, but only below 1150° C. At higher temperatures, it retards the formation of austenite upon cooling, bringing about an excessive formation of ferrite in the heat-affected zones of welds, rendering them too low in impact strength.
• manganese if present in a quantity above 2.0% in the grade causes problems during the production and refining of the grade, since it attacks certain refractories used for the ladles, requiring a more frequent replacement of these costly elements and thus more frequent interruptions in the process.
• Copper an austenite-forming element, is present in a content between 1.6 and 3.0% by weight, and preferably between 2.0 and 2.8% by weight, or even between 2.2 and 2.8% by weight. It participates in the obtaining of the desired two-phase austenite-ferrite structure, making it possible to obtain a better generalized corrosion resistance without being forced to increase the nitrogen level of the grade too much. Furthermore, copper in solid solution improves the corrosion resistance in a reducing acid environment. Below 1.6%, the nitrogen level needed to have the desired two-phase structure starts to become too large to prevent the surface quality problems of continuously cast blooms, as mentioned above. Above 3.0%, one begins to risk copper segregations and/or precipitations that can cause decreases in the localized corrosion resistance and decreases in impact strength during prolonged use (more than one year) above 200° C.
• Molybdenum a ferrite-forming element
• Molybdenum is an element that is present in the grade in a content between 0.05 and 1.0%, or even between 0.05 and 0.5% by weight
• tungsten is an optional element that can be added in a content less than 0.15% by weight.
• the contents of these two elements are such that the sum Mo+W/2 is less than 1.0% by weight, preferably less than 0.5%, or even less than 0.4% by weight and especially preferably less than 0.3% by weight.
• the present inventors have found that by maintaining these two elements, as well as their sums, below the indicated values, one does not observe any embrittling intermetallic precipitations, which lets one in particular de-constrain the manufacturing process for steel plates or bands by allowing for a cooling of the plates and bands in air after heat treatment or working in the hot state. Furthermore, they have observed that, by controlling these elements in the limits claimed, one improves the weldability of the grade.
• Silicon a ferrite-forming element, is present in a content between 0.2% and 1.5% by weight, preferably less than 1.0% by weight. It is added to ensure a good deoxidation of the steel bath during the production process, but its content is limited by reason of the risk of sigma phase formation in event of a poor-quality quench after hot rolling.
• Aluminum a ferrite-forming element, is an optional element that can be added to the grade in a content less than 0.05% by weight and preferably between 0.005% and 0.040% by weight in order to obtain calcium aluminate inclusions with low melting point.
• a content less than 0.05% by weight and preferably between 0.005% and 0.040% by weight in order to obtain calcium aluminate inclusions with low melting point.
• Vanadium a ferrite-forming element
• Vanadium is an optional element that can be present in the grade in a quantity ranging from 0.02% to 0.5% by weight and preferably less than 0.2% by weight, so as to improve the pit corrosion resistance of the steel. It can also be present as a residual element contributed during the adding of chromium.
• Niobium a ferrite-forming element
• Niobium is an optional element that can be present in the grade in a quantity ranging from 0.001% to 0.5% by weight. It allows one to improve the tensile strength of the grade and its machinability through a better chip breakage, thanks to the formation of fine niobium nitrides of type NbN or niobium and chromium nitrides of type NbCrN (Z phase). One limits its content to limit the formation of coarse niobium nitrides.
• Titanium a ferrite-forming element
• Titanium is an optional element that can be present in the grade in a quantity ranging from 0.001% to 0.5% by weight and preferably in a quantity ranging from 0.001 to 0.3% by weight. It lets one improve the mechanical strength of the grade and its machinability by a better chip breakage, thanks to the formation of fine titanium nitrides. One limits its content in order to avoid the formation of clusters of titanium nitrides formed especially in the molten steel.
• Boron is an optional element that can be present in the grade according to the invention in a quantity ranging from 0.0001% to 0.003% by weight, in order to improve its hot transformation.
• Cobalt an austenite-forming element
• Cobalt is an optional element that can be present in the grade in a quantity ranging from 0.02 to 0.5% by weight. This is a residual element brought in by the raw materials. One limits it chiefly because of maintenance problems which it can cause after irradiation of the pieces in nuclear installations.
• the rare earth elements are optional elements that can be present in the grade in a quantity of 0.1% by weight.
• cerium and lanthanum are optional elements that can be present in the grade in a quantity of 0.1% by weight.
• cerium and lanthanum are optional elements that can be present in the grade in a quantity of 0.1% by weight.
• cerium and lanthanum are optional elements that can be present in the grade in a quantity of 0.1% by weight.
• cerium and lanthanum One limits the contents in these elements because they are liable to form unwanted intermetallides.
• This element limits the content of this element, since it is liable to combine with sulfur to form calcium sulfides which degrade the corrosion resistance properties.
• An addition of magnesium in the amount of a final content of 0.1% can be done to modify the nature of the sulfides and oxides.
• Selenium is preferably maintained at less than 0.005% by weight due to its harmful effect on the corrosion resistance. This element is generally brought into the grade as an impurity of ferromanganese ingots.
• the oxygen content is preferably limited to 0.01% by weight, in order to improve the forgeability and the impact strength of welds.
• Sulfur is maintained at a content below 0.030% by weight and preferably at a content below 0.003% by weight. As seen above, this element forms sulfides with manganese or calcium, the presence of which is harmful to the corrosion resistance. It is considered to be an impurity.
• Phosphorus is maintained at a content below 0.040% by weight and is considered to be an impurity.
• the rest of the composition is made up of iron and impurities. Besides those already mentioned above, one will mention in particular zirconium, tin, arsenic, lead or bismuth.
• Tin can be present in a content below 0.100% by weight and preferably below 0.030% by weight to prevent welding problems.
• Arsenic can be present in a content below 0.030% by weight and preferably below 0.020% by weight.
• Lead can be present in a content below 0.002% by weight and preferably below 0.0010% by weight.
• Bismuth can be present in a content below 0.0002% by weight and preferably below 0.00005% by weight.
• Zirconium can be present in the amount of 0.02%.
• the microstructure of the steel according to the invention in the annealed state, is composed of austenite and ferrite, which are preferably, after treatment of 1 h at 1050° C., in a proportion of 35 to 65% by volume of ferrite and more particularly preferred 45 to 55% by volume of ferrite.
• the index IF should be between 40 and 65.
• the microstructure contains no other phases that would be harmful to its mechanical properties, such as the sigma phase and other intermetallide phases.
• the austenite may have been converted into martensite, depending on the effective temperature of deformation and the amount of cold deformation applied.
• the steel according to the invention can be produced and manufactured in the form of hot-rolled plates, also known as quarto plates, but also in the form of hot-rolled bands, from slabs or ingots, and also in the form of cold-rolled bands from hot-rolled bands. It can also be hot-rolled into bars or wire rods or into profiles or forged pieces; these products can then be transformed hot by forging or cold into drawn bars or profiles or into drawn wires.
• the steel according to the invention can also be worked by molding, followed by heat treatment or not.
• the method according to the invention comprises first procuring an ingot, a slab or a bloom of steel having a composition according to the invention.
• This ingot, slab, or bloom is generally obtained by melting of the raw materials in an electric furnace, followed by a vacuum remelting of type AOD or VOD with decarburization.
• quarto plate In the case of manufacture of plates, one then hot-rolls the slab or the ingot to obtain a so-called quarto plate which generally has a thickness between 5 and 100 mm. The reduction rates generally used at this stage vary between 3 and 30%. This plate is then subjected to a heat treatment of putting back in solution the precipitates formed at this stage by reheating at a temperature between 900 and 1100° C., then cooled.
• the method according to the invention calls for a cooling by quenching in air, which is easier to accomplish than the classical cooling used for this type of grade, which is a more rapid cooling, by means of water. However, it remains possible to carry out a cooling in water, if so desired.
• This slow cooling, in air, is made possible in particular thanks to the limited contents of nickel and molybdenum of the composition according to the invention, which is not subject to the precipitation of intermetallic phases that are harmful to its usage properties.
• This cooling can, in particular, be carried out at speeds ranging from 0.1 to 2.7° C./s.
• the quarto plate can be flattened, cropped and pickled, if one wishes to deliver it in this state.
• the cross section ratio between the starting bloom and the end product is preferably greater than 3, in order to ensure the internal soundness of the rolled product.
• this can be cooled, by quenching in a coil in a water tank at the exit from the rolling mill or by quenching in water in turns spread out on a conveyor after they have passed on a conveyor through a solution furnace at temperature between 850° C. and 1100° C.
• a further heat treatment, in the furnace between 900° C. and 1100° C., can be done optionally on these bars or coils already treated in the rolling heat, if one wishes to accomplish a recrystallization of the structure and slightly lower the tensile strength characteristics.
• the tensile properties Rp 0.2 and R m were determined by the standard NFEN 10002-1.
• the impact strength KV was determined at different temperatures according to the standard NF EN 10045.
• the test consists in finding the turning speed that generates 0.15 mm of flank wear for 15 min of effective machining.
• the test is done in regular turning passes with a coated carbide tip.
• the set parameters are:
• flank wear is measured by an optical system coupled to a camera, at a magnification of ⁇ 32. This measurement is the surface of the worn zone as a ratio of the apparent length of this zone.
• 0.45 mm 3 times the value of VB
• tip failure occurs before obtaining a flank wear of 0.15 mm
• the value of VB 15/0.15 cannot be found; one will then determine the maximum speed for which there is neither flank wear of 0.45 mm nor tip failure in 15 min and indicate as the result that VB 15/0.15 is greater than this value.
• Vc min the minimum cutting speed
• the cutting conditions are:
• Vc min that corresponding to an inflection of the curve.
• the ZFC is the zone of the table bringing together the conditions in f and a p for which the chips are well broken, which is quantified by counting the number of satisfactory combinations.
• the critical current of dissolution or activity was determined, given in ⁇ A/cm 2 in sulfuric acid medium at 2 moles/liter at 23° C. A random potential measurement is first done for 900 seconds; next, a potentiodynamic curve is plotted at a speed of 10 mV/min from ⁇ 750 mV/ECS to +1V/ECS. On the polarization curve so obtained, the critical current corresponds to the maximum current of the peak revealed prior to the passivity region.
• the yield strength limit of the tests according to the invention is quite higher than 450 MPa, unlike what is observed for comparison grade 9, for example.
• the grades according to the invention furthermore all present a good machinability, both in terms of cutting speed and chip breakage zone.
• comparison grades 6 and 7, as well as 11 and 12, whose IU indices are negative do not present a satisfactory cutting speed, while comparison grade 10, whose IU index is greater than 6.0, has an insufficient chip breakage zone.
• the generalized corrosion resistance of the grades according to the invention is very satisfactory, and in particular better than that of comparison grade 8.
• the grades according to the invention are the only ones to bring together all of the properties sought, namely, a good castability, a yield strength limit greater than 400 or even 450 MPa in the annealed state or in solution, a good impact strength on plates and bars of great thickness, preferably higher than 100 J at 20° C. and higher than 20 J at ⁇ 46° C., an elevated generalized corrosion resistance, and a good machinability.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Manufacturing & Machinery (AREA)
• Heat Treatment Of Steel (AREA)
• Heat Treatment Of Sheet Steel (AREA)

Applications Claiming Priority (4)

Related Parent Applications (1)

Related Child Applications (1)

Publications (2)

Family

ID=43858298

Family Applications (2)

Family Applications After (1)

Country Status (12)

Families Citing this family (24)

Citations (6)

Family Cites Families (1)

• 2010
  • 2010-07-07 WO PCT/FR2010/000498 patent/WO2012004464A1/fr not_active Ceased
• 2011
  • 2011-07-05 CA CA2804320A patent/CA2804320C/fr active Active
  • 2011-07-05 DK DK11751621.1T patent/DK2591134T3/en active
  • 2011-07-05 US US13/808,284 patent/US9587286B2/en active Active
  • 2011-07-05 EP EP11751621.1A patent/EP2591134B1/fr active Active
  • 2011-07-05 WO PCT/FR2011/000394 patent/WO2012004473A1/fr not_active Ceased
  • 2011-07-05 JP JP2013517431A patent/JP5972870B2/ja active Active
  • 2011-07-05 ES ES11751621.1T patent/ES2534930T3/es active Active
  • 2011-07-05 CN CN2011800337876A patent/CN103069031A/zh active Pending
  • 2011-07-05 BR BR112013000264-6A patent/BR112013000264B1/pt active IP Right Grant
  • 2011-07-05 AU AU2011275610A patent/AU2011275610B2/en active Active
  • 2011-07-05 SI SI201130461T patent/SI2591134T1/sl unknown
  • 2011-07-05 KR KR1020137003293A patent/KR20130034044A/ko not_active Ceased
  • 2011-07-05 CN CN201610471326.1A patent/CN106119737A/zh active Pending
• 2017
  • 2017-01-18 US US15/409,348 patent/US9797025B2/en active Active

Patent Citations (9)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events